The invention described herein may be manufactured and used by or for the United States Government for Governmental purposes without the payment of any royalties.
The present invention generally relates to magnetic sensor methods and systems. The present invention also relates to probing devices associated with magnetic sensors. The present invention additionally relates to spin-dependent tunneling (SDT) sensors.
Magnetic films are used in a variety of devices that include magnetic random access memories MRAM and magnetic recording media. In the magnetic recording industry, information is generally stored as magnetic bits on thin ferromagnetic films. In reading such magnetic bits, the magnetic recording industry requires detection devices that measure the magnetization of small regions along a magnetic track. Computer storage devices, such as, for example, magnetic disk drives, utilize read/write-heads to store and retrieve data. A write head stores data by utilizing magnetic flux to set the magnetic moment of a particular area on a magnetic media. The state of the magnetic moment is later read by a read head, which senses the magnetic fields.
Presently, quality read heads utilize giant magnetoresistance (GMR) read heads, which are spin valves or similar to spin valves. Such GMR thin-film read heads employ magnetoresistive material, generally formed in a layered structure of ferromagnetic magnetoresistive and non-ferromagnetic nonmagnetoresistive materials, to detect the magnetic moments of the data bits on the media. A sensing current is passed through the magnetoresistive material to detect changes in the resistance of the material induced by the data bits as they pass the read head. Spin valves can be formed as three layer structures including a hard or pinned ferromagnet, a soft ferromagnet, and a thin intervening conductor.
Another device for measuring local magnetizations is a magnetic force microscope. Magnetic force microscopes are scanning tunneling microscopes with ferromagnetic tips.
The present inventor has recognized that a need exists for improved systems and methods for probing the magnetic properties of materials. In particular, the present inventor believes that a need exists for improved methods and systems for measuring the extent to which a local surface region of a material can be magnetized. Prior art magnetic sensing systems and methods are limited because most other magnetic probes do not measure how easily a material may be magnetized. Further, most other devices do not readily permit varying the length over which the material""s magnetic properties are being probed.
Other methods for measuring local magnetization such as magnetic force microscopes and electron microscopes with magnetic electrodes that analyze the spin direction of tunneling electrons can be cumbersome, inefficient, and expensive. The present inventor has therefore devised a unique solution to these problems to effectively probe the magnetic properties of a particular material.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to, the present invention and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
It is, therefore, one aspect of the present invention to provide for systems and methods for probing the magnetic properties of materials.
It is another aspect of the present invention to provide an improved magnetic sensor for probing the magnetic properties of materials.
It is another aspect of the present invention to provide a device for use as a magnetic recording read head for magnetic recording media in which the bits can be stored as soft and hard magnetic ferromagnetic material or as magnetic and/or non-magnetic material.
The above and other aspects can be achieved as is now described. Systems and methods for probing the magnetic properties of a material are described herein. A sensor unit can be configured to comprise magnet layers thereof, including a soft ferromagnetic layer, a first hard ferromagnetic layer and a second hard ferromagnetic layer. An intermediate layer, which can comprise an insulator or a conductor, can be disposed between the first hard ferromagnetic layer and the soft ferromagnetic layer within the sensor unit. Additionally, a spacer layer can be disposed between the soft ferromagnetic layer and the second hard ferromagnetic layer, wherein the sensor unit measures the magnetic properties of a material located a distance from the sensor unit through the magnetic interaction of the magnetic layers of the sensor unit. If there is an insulator between the soft ferromagnetic layer and the first hard ferromagnetic layer, then conduction between the first hard ferromagnetic layer and the soft ferromagnetic layer generally occurs via tunneling. If there is a conductor insulator between the soft ferromagnetic layer and the first hard ferromagnetic layer, then the conduction occurs in the plane of the layers and the three-layer structure composed of the soft ferromagnetic layer, the first hard ferromagnetic layer, and the intervening conductor functions as a spin valve.
Additionally, the thickness of the spacer layer and the thickness of the second hard ferromagnetic layer are respectively greater than the thickness of the insulating or conducting layer and the thickness of the second hard ferromagnetic layer. A magnetic interaction generally occurs between the second hard ferromagnetic layer and the soft ferromagnetic layer
The magnetic interaction will increase if the thickness of the spacer layer is approximately equal to the distance to a magnetic surface or film with an appreciable magnetic permeability. This magnetic interaction can thus modify the magnetization of the soft ferromagnetic layer. When the magnetic interaction to the magnetic surface is reduced, the magnetization of the soft ferromagnetic layer should return to its original value. This can be accomplished by configuring the original direction of the magnetization of the soft layer by shape anisotropy or through the application of a biasing field.
In addition, if there is an insulator between the soft ferromagnetic layer and the first hard ferromagnetic layer, then a change in magnetization of the soft ferromagnetic layer results in a change in impedance between the first hard ferromagnetic layer and the soft ferromagnetic layer. If there is a conductor insulator between the soft ferromagnetic layer and the first hard ferromagnetic layer, then a change in magnetization of the soft ferromagnetic layer results in a change in impedance of the spin valve.